160 THE HYGIENE OF THE CIRCULATION 



that the valves do not close the tubes, and consequently 

 the venous, circulation in the legs becomes poor. If per- 

 sisted in, especially in later life, the veins become enor- 

 mously swollen and sometimes even burst through the 

 skin. 



Injuries. Further instances of local interference with 

 the proper distribution of the blood are seen in such 

 injuries as bruises, sprains and fractures. Small blood- 

 vessels are broken, and bleeding into the tissues occurs; 

 lymph vessels are also broken, so that the normal return 

 of the lymph is checked. The collection of the blood and 

 lymph in the tissues causes swelling. Further, as a re- 

 sult of the irritation of the injury, the arterioles in the 

 injured part become dilated so that greater quantities 

 of blood go to them, thereby increasing the swelling 

 and causing throbbing pain. In sprains and bruises, 

 the swelling and discoloration may be largely prevented 

 by working the excess of blood and lymph out through 

 the lymph channels by means of gentle rubbing, or mas- 

 sage. In this way, the force necessary to push the blood 

 and lymph which have escaped from their torn vessels 

 back into the circulation through the lymph channels, 

 is artificially given. Less effective treatment for swelling 

 is heat, which causes contraction of the blood-vessels; 

 cold (ice), which has a similar, although less marked 

 effect; or elastic pressure obtained by bandaging the 

 injured part. 



Inflammation. In inflammation, as in boils and ab- 

 scesses, the blood-vessels are dilated by the irritation of 

 the microbes which have invaded the tissue. Because of 

 this dilatation, the lymph and white blood corpuscles 

 escape more freely into the tissues, where they collect 

 in such great numbers as to clog and distend them. The 

 swollen tissue presses UDon the blood-vessels so strongly 



